The arts minister Ed Vaizey, who said the necklace was 'of great importance for the study of the history of jewellery'. Photograph: Martin Argles for the Guardian

The arts minister Ed Vaizey has placed an export bar on a rare gold and peridot necklace which shines a fascinating light on the troubled and tragic life of a woman who is now seen as something of a forgotten princess.

When Princess Charlotte, the daughter of the Prince Regent, died giving birth aged 21 in 1817 there was an outpouring of national grief not exceeded until the death of Diana.

Now a necklace given by her father, who became George IV, is heading abroad unless an institution or individual comes up with £150,000, or a serious intent to raise it, by 1 July.

The necklace was sold by Yorkshire monks last year and in deferring an export licence Vaizey said it was "of great importance for the study of the history of jewellery and I hope a UK buyer comes forward to secure it for the nation".

The decision was recommended by a reviewing committee chaired by the Tory peer Lord Inglewood. He said: "High-quality jewellery of this age with a provenance as historic and rare as this is a very remarkable survival. It is equally an important example of late Georgian aristocratic taste which is perhaps considerably less 'bling' than its contemporary equivalent might be."

Most of its importance is the story behind it. It was given by the Prince Regent to a Miss Cotes, a present in gratitude for her role in chaperoning his difficult daughter, Princess Charlotte, who, aged 18, was engaged in a battle of wills over her intended marriage.

George wanted her to marry Prince William of Orange. Possibly seeing how much her own parents despised each other after their arranged marriage, Charlotte refused, running away to her mother on the night of 11 July.

The next day she capitulated but was then kept under close surveillance by a team of women who included two dowager countesses, Lady Ilchester and Lady Rosslyn, a governess called Mrs Campbell and two nieces of Lady Rosslyn, Charlotte and Lucy Cotes. It is one of those women that the necklace was intended for.

Their responsibilities for keeping watch ended when Charlotte, in 1816, agreed to marry Prince Leopold of Saxe-Coburg. Charlotte is not the best-known royal name but, had she lived, she would have been queen and not Victoria.

The necklace was for the recipient to wear at the royal wedding. Remarkably, it still comes with an original note from George's sister Elizabeth to Miss Cotes which reads: "I write in great haste by command of The P. Regent to beg you accept the set of Chrysolytes which I send with this note. He hopes You will wear it at the Wedding as a proof of his regard."

The jewellery was made by the pre-eminent jewellers of the age, Rundell, Bridge and Rundell, the company that Napoleon promised to the first of his marshals to conquer London.